-I have a world that I have been playing on for half a year or so, i would create backup versions in case a crash happened or I accidentally blew up the whole place. I forgot about the world for about a month and began playing on it again last week. I ran around killing mobs and came across this white thing, it looked like a block but I could pass through it, not to mention it wasn’t off-centre of the block it was on. Later I would find more of these, i did some tests to figure out what it was.
  There’s a glitch I use that when you fly faster than the world can generate, you can see movable and chests before the normal blocks load. It appears to be an entity, since I can see it before the world loads like I could a cow or chicken. When I dig up the blocks under it, it fell, meaning it was affected by gravity. When in a fire it will catch on fire, it will eventually go out though. I cannot horn it or interact with it other than changing the environment. 
I only noticed this after the 1.11.4 update. I can’t be sure it wasn’t there before. I’m going to trunk some more tests on one of these glitches, I want to see if it is affected by water or pistons.-

Edit: I teleported to the location of one and it appeared as a tnt block before turning back to white. These were the remnants of a huge explosion with lots of tnt that glitched out and stayed. (My game crashed during the initial explosion many times)

(Images were inserted but are not in order of which they were taken)